SOME phage-resistant mutants of Escherichia coli are resistant to some colicines, and vice versa1,2. Among mutants selected for resistance to colicine B four different classes result from mutation near the try (tryptophan-requirement) locus: (1) resistant to colicines B and I; (2) resistant to colicines B, I and V and to phage T1; (3) like (2), but tryptophan-exacting, responding also to indole; (4) like (2), but tryptophan-exacting, not responding to indole. The phenotypes of these four… CONTINUE READING